A current method for cooling turbine shrouds employs an air impingement plate which has a multiplicity of holes for flowing air through the impingement plate at relatively high velocity due to a pressure difference across the plate. The high velocity air flow through the holes strikes and impinges on the component to be cooled. After striking and cooling the component, the post-impingement air finds its way to the lowest pressure sink. However, as this spent cooling air travels to the sink, the accumulating spent air crosses the paths of other high-velocity jets of air which are directed to impinge on the component to be cooled. The spent cooling air thus accumulates in a downstream direction toward the low-pressure sink. This cross-flow of the spent air interacts with the high-velocity incoming impingement-cooling air to significantly degrade the effectiveness of the impingement cooling air as it crosses from the impingement plate to the component to be cooled. This degrading effect becomes more significant in the downstream areas of increased mass flow.
In prior U.S. Pat. No. 5,391,052 issued Feb. 21, 1995 and of common assignee herewith, there is provided apparatus and methods for impingement cooling of turbine components, particularly a turbine shroud, using steam as the cooling medium. While the apparatus and methods disclosed in that application afford effective steam cooling of turbine shrouds, there is constant need for improving the steam turbine cooling with a minimum amount of cooling media and further reductions in the detrimental cross-flow effects.